For those who cannot make it, the merit of the Tirtha-yatra would be collected in an indirect manner, as specified in Smritis & Puranas.
1.If one can send an effigy of themselves and if it gets dipped in the holy river by a Tirtha-yatri then the non-Tirtha-yatri gets 1/8th of the Punya (merit)
2.If a person takes bath in the water body in view of accompanying people who are incapacitated (from taking bath) then they get 1/12 of the Punya